What do you mean by CPR?

is a method by which a person who is not breathing on their own is assisted to 'breathe'.

The person performing CPR would compress their chest 30 times repeatedly (acting as an actual mechanical pump like the heart would normally do to pump blood to the rest of the body), this is followed by 2 breaths into the affected person's mouth (airway). This ensures that oxygen is transferred into the lungs and is then picked up by the blood that is circulating, to be delivered to the rest of the body. Another set of 30 chest compressions is then administered followed by another 2 breaths, this process is repeated for as long as possible until the person revives.